Our laboratory is using magnetic fields to alter electron-spin intersystem crossing rates in chemical and enzymatic reactions with radical intermediates to prove the existence of radical reaction pathways. Only enzymes with spin-correlated radical intermediates can be affected by a magnetic field. These magnetic fields can be exogenous (a laboratory electromagnet giving rise to a "Magnetic Field Effect") or endogenous (arising from the nuclear magnetic moment of atoms involved in bond homolysis thereby giving rise to a "Magnetic Isotope Effect"). These effects have been demonstrated in chemical systems before, but our research group is the first to study these effects in enzymatic systems postulated to have spin-correlated radical pair intermediates. Our experimental goals are: (1) To determine the magnetic field dependence of the kinetic parameters and isotope effects on the radical enzymes ethanolamine ammonia lyase, diol dehydrase, lipoxygenase, dopamine-B- hydroxylase, peptidylglycine amidating monooxygenase, phenylalanine hydroxylase, and DNA photolyase. In preliminary experiments, we have demonstrated a magnetic field dependence to the rate of ethanolamine ammonia lyase, lipoxygenase, and peptidylglycine amidating monooxygenase. (2) To determine the effect of a magnetic field on the photolysis of vitamin B-12 (cobalamin) cofactors by laser flash photolysis. Although our primary focus is to develop new techniques for studying enzymes with radical intermediates and contribute to a more complete understanding of the role of magnetic spin chemistry in the enzymes with unpaired electrons, our work will also address the growing question of how environmental magnetic fields might interact with biological systems.